Extracellular or intracellular microelectrode recordings of light- evoked potentials will be used in quantitative studies designed to further delineate retinal mechanisms of vision. Primary emphasis centers upon the Proximal Negative Response (PNR), a local graded potential which seems to provide a relatively pure and experimentally useful index of the activity of amacrine cells. By exploiting the special advantages offerred by mudpuppy (Necturus maculosus) and frog (R. pipiens) retinas for quantitative experiments, this research program sets four major objectives: 1) To quantitatively define some basic relations between the extracellular PNR and the intracellularly-recorded activity of single amacrine cells. 2) To chart the main features of the light adaptation process in the Necturus retina. 3) To study the effects of certain inhibitory blocking agents upon the PNR. 4) To use the PNR to analyze mechanisms of temporal vision with an experimental rationale closely paralleling that used in contemporary psychophysical investigations of human vision.